1. Field of the Invention
The present invention relates to a magnetic disk apparatus, and more particularly, to a magnetic disk apparatus provided with a rotatable carriage supporting a magnetic head and a drive section for rotating the carriage, and a method for manufacturing the same.
2. Description of the Related Art
In general, a magnetic disk apparatus of a rotary actuator type comprises a housing formed by die casting aluminum or the like. A spindle motor, having a magnetic disk on its rotating shaft, and a carriage supporting a magnetic head are mounted on the bottom wall of the housing. The carriage, which is rotatably supported by means of a pivot shaft set up on the bottom wall of the housing, is rotated by of a voice coil motor for use as a drive source. The magnetic head is rotated together with the carriage, and moved onto a desired information track of the magnetic disk.
The voice coil motor generally includes a bottom yoke and a permanent magnet facing at a predetermined distance from each other, a top yoke which supports the magnet and forms a magnetic circuit in conjunction with the bottom yoke, and a coil fixed to that end portion of the carriage on the opposite side of the pivot shaft to the magnetic head. The coil is situated between the bottom yoke and the magnet with fixed gaps between them. when a predetermined control current is caused to flow through the coil, the carriage is rotated around the pivot shaft by an interaction of magnetic fluxes produced individually by the coil and the permanent magnet.
Conventionally, the bottom and top yokes are fixed on the bottom wall of the housing in the following manner. A mounting surface is formed in a predetermined position on the bottom wall of the housing, and the bottom yoke in the form of a plate is mounted on the mounting surface. The mounting surface is planed, in order to prevent looseness of the bottom yoke and position it accurately with respect to the coil on the carriage. A pair of tapped holes are formed individually at the end portions of the mounting surface, and a pair of through holes aligned individually with these tapped holes are formed in the bottom yoke. The top yoke is a plate member whose opposite end portions are bent toward the bottom wall of the housing, thus forming legs. These legs, which rest on the bottom yoke, each have a mounting hole aligned with each corresponding tapped hole. The top and bottom yokes are fixed together to the bottom wall of the housing by screwing fixing screws into the tapped holes through the mounting holes of the top yoke and the through holes of the bottom yoke.
In the conventional apparatus described above, however, the manufacture of the housing requires a process for planing the mounting surface and a tapping process for forming the tapped holes, and these mechanical processes constitute a hindrance to the improvement of productivity.